The front surface of the eye comprises the cornea at the center, the sclera, which is white and surrounds the cornea, and the limbus, which provides the boundary between the cornea and the sclera. For many years, contact lenses were made that covered the cornea, with little overlap onto the sclera. These lenses could be rigid or soft. Rigid lenses provide advantages over soft lenses, such as superior sagital depth control, shape maintenance, and ability to work with problematic eyes, but rigid lenses are generally less comfortable. Hence, soft lenses have become more popular. More recently, rigid lenses have been made of a much higher oxygen permeable materials and have been made sufficiently large to extend some distance beyond the limbus onto the sclera, while maintaining the advantages of rigid lenses. However, such lenses suffer from a difficulty in that they tend to gradually accumulate debris under the lens, become adhered and uncomfortable and cannot be worn comfortably for a long time.